ssh-agent program is a daemon (a process that runs in the background) which stores your passphrases in memory, allowing you to easily access remote servers without typing a passphrase each time.
For our case, we have already created SSH keypairs with
ssh-keygen and used
ssh-copy-id to upload our private keys onto the authorized_keys file on our server. The only problem now is that we must input our passphrase upon every connection. Let's see how
ssh-agent can help automate this task.
To start the
ssh-agent, input the command followed by
$ ssh-agent bash
This will spawn a new bash process, in which
ssh-agent runs in the background and stores the keys in memory. Now we can add our actual keys with
Enter passphrase for /home/user/.ssh/id_rsa: Identity added: /home/user/.ssh/id_rsa (/home/user/.ssh/id_rsa)
If your key is not in the canonical ~/.ssh directory, or has a different filename, type its path directly after the
ssh-add command (e.g.
Congratulations! Now your passphrase has been added to the
ssh-agent, and you will no longer need to input the passphrase. Now try logging into your server.
$ ssh email@example.com
Last login: Mon Dec 21 05:19:49 2015 from 188.8.131.52 [firstname.lastname@example.org ~]$
Remember that once you exit out of the bash terminal spawned with
ssh-agent, your passphrases will be lost and you'll have to run
Sometimes you'll need to check whether the
ssh-agent is running or not. We can do so by checking our processes.
$ ps aux | grep ssh-agent user 2411 0.0 0.0 10616 524 ? Ss 05:35 0:00 ssh-agent bash
To view the keys that have been successfully added to the ssh-agent, use the
$ ssh-add -l 2048 ec:39:69:3d:c4:8b:63:fd:57:a3:78:51:6d:cd:cd:46 /home/user/.ssh/id_rsa (RSA)
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